As described in the art, gut flora consists of microorganisms that live in the digestive tracts of animals, and constitutes the largest reservoir of human flora. The symbiosis between the gastrointestinal tract and the large number of bacteria contributes substantially to normal digestive function. Thus, the gut flora serves as an effective bather against opportunistic and pathogenic micro-organisms, and this ‘colonization resistance’ is one of their most important functions.
The normal flora presents an exceedingly complex equilibrium between the microorganisms that normally reside in the gastrointestinal tract, playing an important role in nutrition, physiology, and the regulation of the host's immune system [Bourlioux, P., et al. Am J Clin Nutr 78(4): 675-83, 2003].
The numbers and species profile of gut flora varies greatly according to the region of the gastrointestinal tract, with the colon as the most heavily populated area. The majority of bacteria are nonsporing anaerobes, of which the numerically dominant are Bacteroides spp. and Bifidobacterium spp., Eubacterium spp., Clostridium spp., Lactobacillus spp., Fusobacterium spp. and various Gram-positive cocci. Bacteria present in lower numbers include Enterococcus spp., Enterobacteriaceae, methanogens and dissimilatory sulphate-reducing bacteria.
The importance of gut microflora is well appreciated. Flora metabolism is involved in the production of vitamins, modulation of the immune system, regulating the development of the gut, enhancement of digestion and absorption, inhibition of harmful species and removal of carcinogens and toxins and producing hormones to direct the host to store fats and in preventing the development of allergies.
Gut flora has a continuous and dynamic effect on the host's gut and the systemic immune systems. The bacteria are key components in promoting the early development of the gut's mucosal immune system in terms of both its physical components and function and continue to play a role in its operation, later in life. The bacteria stimulate the lymphoid tissue associated with the gut mucosa to produce antibodies to pathogens. The immune system recognizes and fights harmful bacteria, but does not act against the helpful/beneficiary species alone, a tolerance developed in infancy.
With respect to immunity, recent findings have shown that gut flora plays a role in the intestinal expression of Toll-like receptors (TLRs), which are a class of proteins that play a key role in the innate immune system. TLRs cause parts of the immune system to repair injury caused by radiation, for example. TLRs also provide the intestinal ability to discriminate between the pathogenic and commensal bacteria.
The human gut is sterile at birth and microbial colonization begins during delivery. The first bacteria to settle in are able to affect the immune response, making it more favorable to their own survival and less so to competing species; thus the first bacteria to colonize the gut are important in determining the person's lifelong gut flora makeup. Microflora development is then dependent on the type of feeding regime given in early life.
Breast-fed infants have a predominance of Bifidobacteria. In breastfed infants, the flora is not only much richer in bifidobacteria but also includes far fewer species liable to be pathogenic [Bourlioux et al., ibid.]. In contrast, formula-fed infants have a more complex flora which resembles that of an adult, in that Bacteroides, Clostridia, Bifidobacteria, Lactobacilli, Gram positive cocci, coliforms and other sepcies are all represented in fairly equal proportions [Yoshioka, H., et al. Pediatrics 72(3): 317-21, 1983]. However, at the time of weaning there is a shift from predominantly facultative aerobic species such as Streptococci and Escherichia coli to mostly obligate anaerobic species. An age-related effect can be observed. The composition of the flora evolves over time, depending on the diet that the infants receive, until it resembles the flora of adults, at around 2 years of age, when it is thought to become fairly stable [Cummings, J. et al. Eur J Nutr 43 Suppl 2: II118-II173, 2004].
The gastrointestinal tract of newborns is sterile, but it becomes colonized immediately after birth with organisms from the environment, mainly from the mother. During vaginal delivery, the contact with the vaginal and intestinal flora is an important source for the start of the infant's colonization [Orrhage K & Nord C E., Acta Paediatr. 88: Suppl (430): 47-57, 1999]. During Cesarean delivery, direct contact of the mouth of the newborn with the vaginal and intestinal microbiota is absent, and environmental bacteria play an important role for infants' intestinal colonization. Some authors have suggested that the composition of the very first human microbiota could have long lasting effects, up to months [Grönlund M M, et al. J Pediatr Gastroenterol Nutr. 28: 19-25, 1999] or even years [Salminen S, et al., Gut, 53: 1388-9, 2004]. The composition of enteric microbiota in early days of life seems therefore to be a very important factor for achieving and maintaining good health in the years to come.
Thus, there is a continuous and growing need for the development of infant formulations that are can mimic the protective effects of human milk, providing for gut microflora composition as much as possible similar to that of breastfed infants.
Most commonly, probiotics are provided (as dietary product) in order to affect the composition of gut flora. In addition, prebiotics may be used. While probiotics are defined according to the World Health Organization (WHO), as living organisms, which when administered in adequate amounts, confer a health benefit on the host [Morais, M. B. and Jacob, C. M., J Pediatr (Rio J) 82(5 Suppl): S189-97, 2006], prebiotics are non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth of one or limited number of bacterial species already resident in the colon having a potential to improve health [Parracho, H., et al. Proc Nutr Soc 66(3): 405-11, 2007]. As such, any dietary component that reaches the colon intact is a potential prebiotic [Cummings et al., ibid.]. A prebiotic-like effect occurs when there is an increase in the activity of healthy bacteria in the human intestine. The prebiotics stimulate the growth of healthy bacteria such as bifidobacteria and lactobacilli in the gut and increase resistance to invading pathogens. Most interest in the development of prebiotics is aimed at non-digestible oligosaccharides such as fructooligosaccharides (FOS), trans-galactosylated oligosaccharide (TOS), Isomalto-oligosaccharide (IMO), xylooligosaccharides (XOS), soyoligosaccharides (SOS), galactooligosaccharides (GOS) and lactosucrose [Cummings et al., ibid.].
A relatively new development in the area of flora enrichment lies in the field of synbiotics. The term synbiotics includes incorporation of a useful probiotic into an appropriate dietary vehicle with a suitable prebiotic [Cummings et al., ibid.].
Several patent applications describe infant formulations, many of which are based on compositions combining source of proteins, source of carbohydrates, source of lipids as well as vitamins or minerals combined with source of microorganism (probiotic) and/or of prebiotic.
WO 2010/003790 describes a nutritional composition comprising free amino acids, carbohydrate source and a lipid source and can be peptide-free or protein-free. The lipid source comprises triacylglycerides enriched with palmitic acid residue at the sn-2 position of the glycerol backbone. The composition is used for treatment of allergic infants or infants with impaired intestinal absorption, for treating, preventing or alleviating such symptoms while improving calcium absorption in the intestinal tract and/or improving the fat absorption in the intestinal tract and/or softening the stool consistency.
WO 2001/41581 (EP 1 237 419) describes an infant formula comprising combinations of at least one protein component, at least one prebiotic component, at least one lipid component comprising triglycerides in which palmitic acid residues make up more than 10% (w/w) of all fatty acid residues present in the triglycerides and at least 30% of the palmitic acid residues are bonded at the sn-2 position of the triglycerol backbone.
WO 2006/019300 describes an infant nutritional composition of protein, fat, carbohydrate, nucleotide component and a negatively charged non-protein component, which mimics the protective effects of human milk particularly against allergies and infections.
WO 2008/005862 and WO2008/005032 describe infant formula comprising of fat, protein, carbohydrate, vitamins and minerals as well as on an as-fed basis: gangliosides, phospholipids, lactoferrin and sialic acid. This formulation is intended for reducing the risk of diarrhea infants, as well as producing gut microflora profile similar to that of breastfed infants.
WO 2004/112507 describes a formula intended for both infants and young children, comprising a source of proteins, a source of carbohydrates, a source of lipids including at least one long chain polyunsaturated fatty acids (LC-PUFA) and probiotics. The formula is used for strengthening natural immune system defects and promoting a healthy mental development.
WO 2004/112509 describes a nutritional composition comprising of specific fats or non-digestible oligosaccharides and at least one microorganism for inducing a pattern of gut barrier maturation similar to that observed with breast-feeding and for further improving gut barrier maturation, ensuring an optimal barrier function in infants and/or maintaining gut barrier homeostasis.
WO2006/108824 describes an infant formula comprising a source of protein, a source of lipids, a source of carbohydrates and a probiotic. The formula is used to modulate the immune system of a neonatal infant to promote the development in the first few weeks of the life of an infant of a beneficial intestinal microbiota comparable to that found in breastfed babies as well as to promote the maturation of the immune system of a neonatal infant in the first few weeks of life.